The natural lens in the eye of a newborn baby is a colorless, transparency, and very soft lens. The ability of the natural lens of newborn baby's eye to change shape and produce dramatic changes in focus is magnificent. As a person ages, the change of external conditions, such as ultraviolet light exposure, the natural lens becomes less clear, more rigid, more color, and functions more like a monofocal lens. When over fifty or sixty years, more than 30 percent of people's crystalline lens will turn yellow or brown or even cloudy. The cloudiness is called a cataract. When this happens, not only lost the accommodative function, but also blurred vision and sensitivity to light. The results will be trouble reading, driving, and less colors vivid when this happens, such natural lens (i.e., the cataract lens) will have to be replaced with an artificial intraocular lens to restore eyesight of the cataract patient.
A typical intraocular lens is comprised of an optical body and a supporting arm, particularly, the optical body focuses light onto the retina of your eye to enable the optical lens to see the object. The supporting arm is used to support the optical zone, so that the optical zone of the lens is at the center of the eye which can be focused effectively.
The optical zone and supporting arm of the intraocular lens can be made of the same material or can be made of different materials. The intraocular lens made of the same material is commonly referred to as a one-piece lens, while the intraocular lens made of different materials is commonly referred to as a three-piece lens, and examples thereof are reported in U.S. Pat. Nos. 4,997,442 and 5,217,491, among these patents, the optical zones are both made of relatively soft optical materials and arm zone are both made of relatively hard materials.
The conventional monofocal intraocular lens can provide vision correction with a conventional distance, but cannot provide an effective adjustable-focus vision correction, besides, the design wavelength is always the detection wavelength, and chromatic aberration cannot be corrected within the visible light range. In other words, it cannot play a role of vision correction both at far and close distances. The only way to make the monofocal intraocular lens work both at far and close distances is to wear a pair of glasses. Another choice is to replace the cataract lens with a multifocal intraocular lens, to make vision at far, close and medium distances available. However, only a part of light at each distance is focused onto the retina of your eye, in addition, multifocal intraocular lens will have some other side effects exist. As a result, people begin to design a novel adjustable-focus intraocular lens, as disclosed in U.S. Pat. Nos. 4,409,691, 5,674,282, 5,496,366, 6,197,059, and 6,387,126, 6,178,878, and 6,406,494. In an accommodating IOL, the loops are designed to keep the IOL securely in place and prevent any rotational movement, but the legs are flexible in a way that allows the optical portion of the IOL to move slightly forward upon contraction of the ciliary muscle. In this fashion, an accommodating IOL can expand the range of clear vision after cataract surgery, providing better near vision without eyeglasses than what is possible with a conventional monofocal IOL procedure. The optical portion of the IOL to move forward and backward distance is heavily rely on the contraction of the ciliary muscle. For some patients, the contraction of the ciliary muscle is too weak, cannot move the optical body of the intraocular lens, the intraocular lens turn to be the conventional monofocal intraocular lens. And also, the accommodative function will turn to weak along with the increase of the implantation time.
All the designed accommodative intraocular lenses are made of a soft silicone material with a low refractive index. Due to the fact of lower the refractive index of the silicone material, the intraocular lens made from it, is relatively thick, the intraocular lens has a limited distance to move within the capsular bag of your eye, resulted some focusing power back to the ageing eye, but will certainly not restore the same level of focusing available in a young person's eye. And also, the intraocular lens made from the silicone material will have a higher possibility to form fibers and secondary cataract than the intraocular lens made from hydrophobic polyacrylic ester material. Therefore, after the adjustable-focus lens made of silicone is implanted into the eye, only a part of people can have the adjustable-focus function, and the percentage of the part of people in the total number of transplanted people is also reduced along with the increase of the implantation time.